This invention relates to methods and apparatus for separating wax particles and/or water droplets from a hydrocarbon oil mixture boiling in the lubricating oil range, in which mixture the wax/water forms a dispersion. The term "wax particles" herein means wax in any particulate form and includes wax crystals. Furthermore, throughout this specification, it is to be understood that "hydrocarbon oil mixture" and "oil mixture" both mean a hydrocarbon oil mixture boiling in the lubricating oil range.
The problems of wax or water in lubricating oil are very well known in the art. In the distillation of crude oil, a proportion of wax is present in cuts taken in the lubricating oil range. Some of the wax remains dissolved in the oil, whereas other fractions form a haze as the oil fraction ages at ambient temperatures or below. Wax in itself is in fact a good lubricant but under comparatively low temperatures such as engine cold start conditions, its presence causes the oil to be thick and viscous and as a result the engine may be hard to turn over at sufficient speed during starting. In the case of water droplets, which include both very tiny water droplets (less than about 1 mm in diameter and exemplified by approximately 1 to 100 micron diameter droplets) and water molecules suspended in the lubricating oil, they detrimentally affect the lubricating properties of the oil and increase engine wear and corrosion. Haze manifests itself as a milky or cloudly appearance in the oil and is usually caused by either water or wax or both water and wax being present in the lubricating oil. Typically a minimum of about 50 ppm. of water or a minimum of about 0.1% by volume of wax will cause some lubricating oils to look hazy. Therefore the existence of haze caused by the presence of water droplets or wax crystals or particles detrimentally affects the performance of lubricating oils. It is of paramount practical importance to devise techniques for removing wax and/or water haze from lubricating oil in a relatively inexpensive, simple and effective manner, which techniques are also capable of implementation on an industrial scale.